You see an investment opportunity at a low price, but you think this has no value on books, so you don't buy it. Later, you see everyone on Twitter talking about the same thing. That is the only thing they seem to be talking about. Surprisingly, now the investment is trading at an all-time high. You don't give in until a credible person talks about it. You think, he knows more than me – if he's saying it, then there must be some value to it. So you eventually buy it – at its highest price. Later, you realise it was all a bubble, and the price comes crashing down to almost nothing.